This invention relates to the production of storage tanks. It is particularly directed to the production of large diameter storage tanks from strip metal.
It is known to produce large diameter storage tanks from strip metal in which the tanks are built upwardly by the feeding of the strip metal to a support assembly arranged circularly on a base and which supports the strip in a helical path. The McDonald U.S. Pat. No. 3,380,147 which issued 30 Apr. 1968 is an example of one such method of producing a storage tank. As disclosed in that patent, one edge of the strip metal is bent and overlapped with the adjacent helical turn which is not bent. Two separate and distinct welds are then completed to join the adjacent helical turns together.
One aspect of the present invention involves the production of a storage tank without edge bending of the steel in any manner. Adjacent edges of helical turns are butt welded together in a single welding operation to join adjacent helical turns of the tank together.
The present invention also involves techniques for handling the steel as the tank is made. In particular, the strip is vertically adjusted to provide for appropriate orientation during the construction process and to ensure a proper spacing of adjacent turns of the strip for welding purposes. A unique yoke assembly may be employed bearing against both the upper and lower edges of the strip metal as it is fed to the support assembly, thus providing for vertical adjustment of the strip both upwardly and downwardly. Spacing of the strip in the area of the welding operation itself may be achieved by spacing devices, such as a spacing disk or wedge-shaped spacer which spaces apart the adjacent helical turns by the predetermined amount necessary for proper welding. The welding itself may be by hand operation, or automatic. A chill roller may be employed on the opposite side of the strip from the welding head to provide a back-up for weld bead formation purposes, and may provide for the addition of a back-up strip to be added to reinforce the weld.
The aligning of the adjacent helical turns of the strip metal as well as the welding may be carried out through use of a support structure which is mounted on the base and which includes two parts, one on the outside of the tank which is being built and the other on the inside. The inside part is collapsible, so that the support structure may be easily withdrawn following the completion of the building of the tank.
The support assembly for the entire tank is advantageously constructed of groups of rollers that are arranged circularly about the base. Each roller group may include support rollers that a support the lower edge of the strip and side support rollers positioned against the inside and outside surfaces of the strip. These support rollers may be mounted on a support bracket which is pivotable about horizontal and vertical axes to provide for varying degrees of orientation of the rollers to accomodate varying pitches of the strip steel and diameters of tanks.
Various construction procedures for the fabrication of tank tops as well as bases for tops and bottoms of tanks are disclosed.
The invention will be more completely understood by reference to the following detailed description, taken in conjunction with the drawings.